The Mongrel Mob Defence app, available on Google Play, was launched on Friday by developer Supremacy.

The app allows the player to pose as a Mongrel Mob member protecting his gang pad from Black Power.

While the app has earned a 4.7 star rating from its users, former gang member Denis O'Reilly says it's irresponsible.

"It's potentially dangerous if people confuse reality and online stuff," he told Newshub.

"We've spent a lot of time in New Zealand getting people not shooting each other in family houses."

Mr O'Reilly says gangs will not be impressed, and he doesn't know anything about Supremacy as a company.

"Is this some white organisation from America? Are these Russians having a go at us?"

The game presents users with a caricature of deceased Mongrel Mob member Greco, which is made up of a real photo of the late gang member.

The image is superimposed to include the gang member wearing an iconic Mongrel Mob T-shirt and red Croc shoes, as well as holding two pistols.

Greco's photo was taken by photographer Jono Rotman in 2008 during a series of portraits he took of Mongrel Mob members.

Mr Rotman was unavailable for comment, but has threatened legal action against Supremacy if the image is not removed, which Mr O'Reilly says the developers should take seriously.

"Rotman, who mixes with our brotherhoods, is fastidious about getting permission for images, so be scared of my friends and other friends but be terrified of Jono Rotman."

In response, Supremacy told Newshub the game was intended as a "comic time-waster", but to avoid causing further offence they will change the character's image to Alf Stewart from Australian soap Home and Away.